RED - addChild to the root. Not implemented.
GREEN - Added the child to the root children list.
RED - Try to get a node from 2 levels below the root.
GREEN - Changed so it was not always added to the root but the parent node.
REFACTOR - Cleaned up code and changed some javadoc..
RED - Add a child with null parent.
GREEN - Check for null parent.
REFACTOR - Cleaned up the TreeTest class and updated the Tree class.
RED - Try to add a child that is null.
GREEN - When adding a child that is null it will throw a NullPointerException.
REFACTOR - Combined the if statements and updated javadoc that if a child is null it will throw a NullPointerException.
RED - Tried to create a tree with the root is null, should throw a NullPointerException.
GREEN - When creating a tree with the root is null, it throw a NullPointerException.
REFACTOR - Updated javadoc and the message that will follow the NullPointerException.